The present inventions relate generally to packaging for optical switches.
In recent years there have been extensive efforts to develop commercially viable optical switches. Presently there are a few relatively small optical switches on the market (e.g. eight port switches). There are also on-going efforts to develop larger optical switches (e.g., switches having 64 to thousands of ports). One proposed optical switch architecture contemplates the use of arrays of Micro Electro-Mechanical Systems (MEMS) mirrors to accomplish the switching. A perceived advantage of this approach is that it is potentially scalable to many channels. One such MEMS mirror based optical switching system is diagranmatically represented in FIG. 1(a).
In the embodiment shown, the optical switch 5 includes an input fiber array 10, an input lens array 11, input and output mirror arrays 12, 13, an output lens array 14 and an output fiber array 15. The input and output fiber blocks 10, 15 each consists of a two dimensional array of fibers with a polished end face. The input fiber block 10 is positioned adjacent an input lens array 11 to provide collimated input beams, while the output lens array 14 is positioned adjacent output fiber block 15 to provide collimated output beams. Each mirror in the input and output mirror arrays is rotatable about two orthogonal axes so that an input beam received on any one of the input fibers can be directed towards any one of the output fibers by appropriately adjusting the orientation of their associated mirrors.
In theory, the mirror arrays can be formed using a wide variety of techniques and different companies have adopted different approaches in their attempts to provide suitable mirror arrays. By way of example, one approach is to create movable mirrors by forming MEMS structures on a monolithic silicon substrate. Devices such as these are commercially available from a variety of sources including MCNC of Research Triangle Park, N.C. and Analog Devices of Cambridge, Mass.
In some implementations, the mirrors are actuated electrostatically. In the configuration illustrated in FIGS. 1(a) and 1(b), each mirror is rotatable about two orthogonal axes. The mirrors have an equilibrium position, from which they rotate bidirectionally about the respective axes. Since electrostatic actuators ordinarily can move a mirror in only one direction from equilibrium, four electrodes are typically needed to actuate each mirror in each array and eight electrodes are needed per switch channel. Consequently, a very large number of electrical interconnections are needed to drive a large optical switch.
Another common optical switch configuration is illustrated in FIG. 1(b). In this configuration, a xe2x80x9cfoldedxe2x80x9d optical path is provided by using a fixed mirror 25 that cooperates with a moveable mirror array 27 (which may be implemented as a single mirror array or multiple mirror arrays) so that an input beam is reflected first off of an associated input mirror in moveable mirror array 22. The first mirror directs the beam to reflect off of the fixed mirror 25 to an output mirror associated with the desired output channel. With this arrangement, all of the moveable mirrors can be placed on the same xe2x80x9csidexe2x80x9d of the optical switch while the input and output fiber arrays can be placed together on the other side of the optical switch.
Regardless of which of the described (or other) approaches is used, the mirror arrays must be packaged in a manner that provides the required number of electrical interconnections. A rigid mechanical structure is also required to accurately align the optical components. In one proposed implementation, the mirror arrays are mounted on a rigid metal structure, while the electrical interconnections are provide by other means such as a flexible electrical cable. A difficulty with this approach is that the electrical cables that are large enough to provide the number of interconnections needed in a large optical switch are not very flexible. This problem is accentuated by the requirement that the traces must be relatively widely spaced due to the high voltages needed to drive current MEMS based electrostatic actuators (typically 100V or more today, although these requirements are expected to decrease as the technology develops). The silicon substrates are quite fragile and there is a danger that the stiffness of the required cables might damage the MEMS mirror arrays through mechanical stress if the interconnecting cables were attached directly to the mirror arrays. Accordingly, there is a need for improved packaging arrangements for optical switches.
To achieve the foregoing and other objects of the invention, a variety of improved optical switch packaging techniques and optical switch components are described. In one aspect of the invention, an optical switch component that includes a die mounted on an interposer is described. The die has an exposed array of mirrors that can be used as part of an optical switch. Typically, the interposer will also have a fiber array mount arranged to receive a fiber array and to position the fiber array appropriately over the array of mirrors. The interposer may also carry electrical connectors suitable for electrical connection to external devices. In this arrangement, bond pads on the die are electrically connected to the electrical connectors through appropriate conductive features on the interposer.
In some embodiments, the contact pads are positioned around an opening in the interposer and the array of mirrors is exposed through the interposer opening. In one preferred implementation, the die is attached to the interposer by directly metallurgically joining bond pads on the die to associated contact pads on the interposer. In another embodiment, the die is attached to the interposer and wire bonding is used to facilitate the electrical connection between the die and interposer.
In another aspect of the invention, the fiber array mount carried by the interposer includes a base, an alignment stage and a bracket. The base has an alignment ridge and the alignment stage has a stage slot therein that fits over the alignment ridge. The stage also includes a ledge within the slot. The bracket is sized to fit into the slot and has a bracket ledge arranged to rest on the stage ledge within the slot. The bracket also includes a bottom surface recess arranged to nest over the alignment ridge within the slot. Fasteners are provided to couple the bracket to the base to hold the alignment stage and base together.
In many of the described embodiments, an optical switch can be formed by putting together two of the described interposer based optical switch components. In some embodiments the two components may be mirror images of one another, although this is not a requirement. When placing two interposer based optical switch components together, an alignment frame may be positioned between the interposers to help maintain a desired spacing between the respective arrays of mirrors. In some such embodiments, the alignment frame may be arranged to rest directly on the interposers and to surround the dice and fiber arrays.
In other embodiments of an optical switch, an inner housing is provided that encloses the dice, the fiber array mounts the alignment frame and portions of the interposers, but leaves the connectors exposed. In one preferred implementation incorporating a housing, the inner housing is sealed and a seal is formed between the inner housing and the respective interposers by soldering the inner housing directly to the interposers. A heater or cooler may optionally be provided to heat or cool the inner housing.
In various embodiments, the fiber bundle is a collimated array of optical fibers. Ribbon cables may be coupled to the interposer connectors, with each ribbon cable having an external connector for connecting to external systems.
In another aspect of the invention, an optical switch is provided which has an outer housing in addition to the inner housing. The outer housing encases the optical switch components and the inner housing and a resilient filler material is provided between the inner and outer housings to provide additional protection to the optical switch.